Year 7 Ratio Map Scale Dr J Frost

Year 7 Ratio & Map Scale Dr J Frost (jfrost@tiffin. kingston. sch. uk) www. drfrostmaths. com Objectives: Understand what ratio means, simplify ratios, and solve problems involving values within a ratio. Last modified: 18 th May 2016

Stand up if… You have two colours to pick from only. Red Blue Stand up if you prefer (a) Red (b) Blue Suppose the results were the following: Red 18 Blue 12 Suppose also we were unconcerned by exact numbers who voted for each but wanted to express the relative size of how many voted for each. What ways could we do this? Percentages: Ratio: Red 60%, Blue 40% ? Percentages are good for indicating proportion of some total. Ratio of red to blue: ? 3: 2

What is ratio? For each three people who chose What specifically does this mean? red, two chose blue. Quick Test of Understanding: 1 The ratio of monkeys to squirrels is 3: 7. If there are 6 monkeys, how many squirrels are there? If for each 3 monkeys there are 7 squirrels, then if there are twice as many monkeys, there are twice as many ? squirrels, i. e. 14. 2 Simplify the ratio 12: 16. 3: 4 ?

Common Types of Questions The ratio of muffins to cupcakes in a cake sale is 3: 1. There’s 20 cakes in total. How many muffins are there? In a death match of monkeys vs squirrels, the monkeys outnumber the squirrels by a ratio of 5: 2. There’s 35 monkeys. How many squirrels are there? Bro Tip: Carefully reflect on what the number given (here the 20) represents in the ratio. Here the 20 represents the TOTAL parts. Possible method: Identify what 1 ‘part’ is worth: ? 4 parts = 20 1 part = 5 ? 3 parts = 15 ? Therefore 15 cupcakes. 5 parts = 35 1 part = 7? 2 parts = 14 Therefore 14 squirrels.

Further Example Alice and Bob share some money in the ratio 7: 4. Alice received £ 12 more than Bob. What did they receive in total? 3 parts = £ 12 1 part = £ 4 11 parts = £ 44 ? This time £ 12 represents the DIFFERENCE in the parts. We want the total amount, so need to find the value of the total parts.

Test Your Understanding 1 The ratio of cats to dogs at Battersea Dogs & Cats home is 2: 3. There are 45 animals in total. How many cats are there? 2 The ratio of Tiffin Boys students to Tiffin Girls students is 8: 9. There’s 2700 students at Tiffin Girls. How many at Tiffin Boys? 2400 ? 18 ? 3 Tom, Dick and Harry share some money in the ratio 4: 7: 2. Dick receives £ 35 more than Harry. How much did Tom and Dick receive in total? £ 77 ?

PUZZLES (working in pairs) 1 3 ? ? 2 ?

Exercise 1 1 Simplify the following ratios: 2: 6 = 1: 3 ? 10: 15 = 2: 3 ? 24: 18 = 4: 3 ? 56 : 49 = 8: 7 ? 2 3 (on provided worksheet) What is the ratio of shaded to nonshaded triangles? 1: 3 ? If £ 30 is split between two people in the ratio 3: 2, what does each get? £ 18, £ 12 ? 4 5 ? 6 ? 7 To make orange squash I mix concentrate and water in the ratio 2: 7. If I use 150 ml of concentrate, how much water do I use? 525 ml ? ? 8 ?

Exercise 1 (on provided worksheet) 9 13 ? 10 ? ? 11 14 ? 12 ? ?

Exercise 1 15 (on provided worksheet) N ? 16 [STMC Final 2007/08 Q 1] Anne, Becky and Charlotte had sums of money in the ratio 7: 6: 5. One of them gave £ 9 to one of the others and this changed the ratio (in the same order of names) to 6: 5: 4. The total sum of money remained the same; what was it? Solution: ? £ 810 ?

You have a map of Kingston-upon-Thames… Scale 1: 300 What does this scale mean? It means that 1 cm on the map ? represents 300 cm in real life. (Note the units had to be consistent) 75 cm Tiffin John Lewis What distance is this in real life? ?

Examples 1 ? 2 ? 3 ? Bro Tip: When scaling a length you’re still in the same unit!

Test Your Understanding 1 ? 2 ? 3 ?

Further Practice 1 ? ? 2 ? 3 ?